(1) Field of the Invention
The present invention relates to method and apparatus for detecting the ignition timing for a Diesel engine, and more particularly, to a method for detecting the ignition timing of the Diesel engine and an apparatus for detecting the ignition timing of the Diesel engine from the output signal from a combustion light or burning flame sensor provided within the combustion chamber of the Diesel engine.
(2) Description of the Prior Art
In the field of art concerning the Diesel engines, there have been proposed some systems for detecting the start of ignition of the engine and for controlling the fuel injection timing and fuel injection amount. One of the systems is such that the ignition timing of the Diesel engine is detected by detecting a burning flame of the engine and the fuel injection timing and amount are controlled by utilizing the result of the detection. In such system, an ignition signal is produced from the light radiated from the burning flame of the engine and the time when the ignition signal is produced is determined as follows.
Namely, a crank angle signal which is periodically produced at a predetermined crank angle position, for example, a crank angle signal producing at every crank angle of 1.degree., is frequency-multiplied to produce a pulse signal which develops at each angle of 0.1.degree., and a time interval from a predetermined reference position until the ignition signal produced, is detected and measured by counting the pulse signals.
However, such system mentioned above requires (1) a crank angle sensor for detecting and producing a crank angle signal developed at every crank angle of, for example, 1.degree. and (2) a signal processing circuit for dividing the frequency of the signal from the crank angle sensor; therefore, complicated sensor and signal processing circuit are required, which leads to increased manufacturing costs for such a device for realizing the system.
On the other hand, with respect to an apparatus for detecting the ignition of the fuel injected, a feedback technique is utilized which precisely controls the fuel injection timing and fuel injection rate or amount in accordance with the fuel ignition state, in which a flame sensor for detecting the ignition state of the fuel is used. Normally, the flame sensor has a cylindrical housing within which a light guide made of a heat-resistant, light-transmissive material such as quartz glass is fitted to. The light guide has a detection end which is slightly projected out of the cylindrical housing, the detail of which will be described later.
The combustion light or the burning flame detected by the flame sensor is led out of the combustion chamber and converted into an electrical signal by photoelectric converting means such as photodiodes, phototransistors or solar cells. However, the fuel is not necessarily combusted at a time point after the ignition is started and there is a case that one injection of the fuel is followed by two combustion strokes, or one combustion stroke provides two combustion light or burning flame detection signals. As a result, the control of fuel injection timing and amount could not be precisely done in accordance with the detection signals, in the technique according to the prior art.
To overcome such problems, it has been proposed to read the time interval from one signal to another when plural signals are supplied as input and to interpret plural signals as one signal if the time interval between such plural signals is judged to be within a predetermined value. Another method has also been disclosed in which combustion flame detection signals for such plural combustion strokes are cancelled. In the former case, however, the time interval between detection signals which may be taken as one signal varies with the change of engine speed, with a disadvantage that the construction of the signal reader is complicated or that control by a microcomputer needs complicated programs. The latter method is also disadvantageous in that control cannot be precisely effected.